Liquid fuel circulating system for mechanically atomizing liquid fuel burner and method of controlling the output of said burner



Feb. 22, 1955 T. B. STILLMAN LIQUID FUEL CIRCULATING SYSTEM FOR MECHANICALLY ATOMIZING LIQUID FUEL BURNER AND METHOD OF CONTROLLING THE OUTPUT OFSAID BURNER Filed Sept. 8, 1949 4 Sheets-Sheet 1 H mama im? l N mf ucmR 50 38 0 V5 Xmfl m E A 5 8 a m m m h F. T nww 1 W F 5 Feb. 22, 1955 T. B. STILLMAN 2,702,590

LIQUID FUEL CIRCULATING SYSTEM FOR MECHANICALLY ATOMIZING LIQUID FUEL BURNER AND METHOD OF CONTROLLING THE OUTPUT OF SAID BURNER Filed Sept. 8, 1949 4 Sheets-Sheet 2 INVENTOR 7710mm; 5 Stfl/mam Deceased 5v. E Z 0156 B5ZW/ma/2,

Exe cuirlx FIG. 3

ATTORNEY Feb. 22, 1955 T. B. STILLMAN 2,702,590

LIQUID FUEL CIRCULATING SYSTEM FOR MECHANICALLY ATOMIZING LIQUID FUEL BURNER AND METHOD OF CONTROLLING THE OUTPUT 0F SAID BURNER 4 Sheets-Sheet 3 Filed Sept. 8, 1949 WWW 70 INVENTOR Thomas BSti/Zman,

Deceasd .7 B Elo/se fl'tz'llman 55 BY Execuir/x ATTORNEY Feb. 22, 1955 T B sTlLLMAN 2,702,590

LIQUID FUEL CIRCULATING SYSTEM FOR MECHANICALLY ATOMIZING LIQUID FUEL BURNER AND METHOD OF CONTROLLING THE OUTPUT 0F SAID BURNER Filed Sept. 8, 1949 4 Sheets-Sheet. 4

L /e 0050 Q L65 0F 0/1 BUP/VfD/BUP VBQ/HOUR INVENTOR Thomas 5 Stil/mam Deceased 5v 20156 5 Stz'i/mam Execu ir/x ATTORNEY United States Patent LIQUID FUEL ClRCULATING SYSTEM FOR MECHANICALLY ATOMIZING LIQUID FUEL BURNER AND METHOD OF CONTROLLING THE OUTPUT OF SAID BURNER Thomas B. Stillman, deceased, late of South Orange, N. .L, by Eloise B. Stillman, executrix, South Orange, N. J., assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application September 8, 1949, Serial No. 114,568

5 Claims. (Cl. 158-363) This invention relates to wide-range return-flow mechanical fuel burner atomizers and, more particularly, to a novel system for and method of controlling the liquid fuel supply to such atomizers in a manner to obtain high combustion efficiency over a wide range of operation and to concurrently assure good mechanical and hydraulic performance of the fuel supply system.

It has been found desirable, in practice, to operate fuel burning systems over a wide range by utilizing a relatively small number of large capacity liquid fuel burners over the entire range rather than by selectively varying the number of burners in operation in accordance with the fuel demand. In addition, it has been found practically advantageous to provide multiple burner installations which can be operated under automatic control throughout a wide capacity range. These considerations have led to the use of wide range return-flow liquid fuel burner atomizers of different constructions and with different methods of and apparatus or systems for control thereof.

These atomizers and related fuel supply and control systems have not been without some disadvantages. For example, it has been found necessary, with some types of installations, to manually or otherwise change the position of the atomizer relative to the burner throat opening in order to avoid carbon deposition upon the throat and impeller, with consequent loss in combustion efliciency, at the lower rates of operation. Other disadvantages, such as an excessive delivery of hot oil from the return passage of the atomizer to the storage tank, have involved the danger of vapor flashing in the supply pump. It has also been found that, when the recirculated oil is introduced at variable pressure to the oil inlet of the pump supplying the atomizer, mechanical difliculties in attaining proper sealing of the pump have been experienced.

In a mechanical type of liquid fuel atomizer, the fuel is directed inwardly to a cylindrical whirl chamber through tangentially arranged passages of small crosssectional flow area to set up a swirl of high angular velocity in the chamber, and the swirling liquid is discharged into the furnace through an atomizing orifice positioned centrally of the chamber end wall. The liquid as it flows through the orifice thus has both angular and axial velocity as related to the orifice axis, and is thrown outwardly as atomized particles in a spray of conical configuration. For a given weight of oil flow through an orifice of fixed size, the apex angle of the spray cone is proportional to the angular velocity of the fluid discharged through the orifice. If the apex of the spray cone is maintained at a fixed axial position relative to the axis of the burner port associated with the atomizer whirl chamber, the width of such apex angle has a direct bearing on the proximity of the spray cone to the burner port.

The proximity of the projected spray cone to the embracing burner port is also affected by the velocity of the combustion air which is discharged in embracing relationship inwardly to the furnace. With a selected ratio of cross-sectional flow area of the tangential passages and orifice, for an advantageous wide cone angle at maximum capacity, the relative angular and axial velocities will vary to substantially the same extent so that, in so far as the angle of the cone is determined by the force resulting from velocity and pressure conditions in the whirl 2,702,590 Patented Feb. 22, 1955 ice chamber, the cone angle will remain substantially the same, and contact of the outer atomized particles with the burner opening throat will be avoided with the corre lated flow of combustion air.

When a wide-range high capacity return-flow atomizer having tangential passages and whirl chamber sizes selected for efficient operation at maximum capacity is in operation with a reduced fuel input to the furnace, impingement of atomized fuel particles from the outer portion of the cone upon the burner opening throat will usually occur at the lowermost portion of the fuel input range unless the atomizer is axially advanced toward the furnace from its maximum rate position. This occurs because the return-flow atomizer has a return flow passage leading from its whirl chamber, whereby a portion of the fuel delivered into the whirl chamber is drawn off, leaving the remaining portion of the fuel entering through the tangential passages to be discharged through the orifice. Thus, with this type of atomizer the angular velocity component of the orifice discharge, which is a function of the flow through the tangential passages, does not decrease as rapidly with reduction in atomizer delivery as does the axial velocity component which is a function of the delivery rate. If the liquid fuel is supplied to the outer ends of the tangential passages at constant pressure and the rate of delivery through the atomizing orifice is controlled by regulation of the return-flow draw-01f, the modification in whirl chamber pressure will be such that, at the lowermost portion of the atomizer range, the pressure of the whirl chamber will be substantially reduced, while the velocity through the tangential passages and the angular velocity will remain without effective change. This lower range of atomizer delivery results in a greater spray cone angle and impingement as before mentioned.

The main object of the present invention is the pro- VlSlOll of apparatus for and a method of operating a wide range return-flow mechanical liquid fuel atomizer whereby the angle of spray or atomization may be controlled with variable rates of fuel atomization so that carbon deposition may be avoided without modifying the axial position of the atomizer relative to the furnace or burner throat, while at the same time providing an arrangement of piping, and pumping and control apparatus, effective to regulate the quantity of oil recirculated in the system to the end that undue heat input into the oil storage will be avoided, and the pump handling hot oil will receive 011 at a pressure sufiiciently uniform that the seal difiiculties due to pressure variation are eliminated.

In the present invention, the flow of the liquid fuel through the tangential passages is effectively regulated along with a regulation of the return-flow draw-off from the whirl chamber so that, for reduction in atomizer delivery rate, a reduction in the differential in pressure between the inlet and discharge ends of the tangential passages is effected, while the pressure in the whirl chamber is controlled in correlation with the differential to the end that the angular velocity of delivery is correspondingly decreased to the extent that the spray cone angle will not be disadvantageously increased at the lowermost fuel delivery rate.

To effect this result and to provide an atomizer of good efliclency for a wide-range of fuel burning capacity, a ratio of tangential passage and orifice areas is selected such that, at the selected fuel supply pressure for maximum delivery, all of the fuel delivered through the tangential passages is delivered through the orifice, with the return-flow outlet shut-off.

For operation below maximum delivery rate, both the pressure of the fuel delivered to the outer ends of the supply passages and the pressure in the whirl chamber are reduced and, with progressive reduction of delivery, the reduction is carried still further. The rate of reduc tion of the supply pressure is related to. the rate of reduction of the whirl chamber pressure, so that the differential between these pressures will be of a variable degree, being maximum at the high fuel input rate and progressively smaller toward the low fuel rates.

The invention method of regulation effects not only an eflicient atomization of fuel over a wide range of fuel input rates without a disadvantageous spread of the spray is operating at minimum whirl chamber pressure.

cone at the lowermost load range, but also it is advantageous in that it minimizes the amount of oil which is delivered through the return-flow draw-off, as the whirl chamber pressure is at a lower pressure for a given fuel delivery than if the control were solely by regulation of return-flow draw-off. This is an advantage in reducing the heat carried back to the oil reservoirs by the returnflow fuel. The pump which draws oil from the reservoir will thus not be required to handle oil of excessive temperature with the consequent hazard, to its continuous delivery, of vapor flashing.

Additionally, when high liquid fuel supply pressures to the atomizer are indicated as necessary to attain an exceedingly wide delivery rate range, and it is desirable to use two pumps in series to develop such pressures, the return fuel flow stream may be introduced to the inlet side of the high pressure pump if the low pressure pump is selected to have a maximum delivery pressure below the minimum pressure of the return oil when the atomizer With such an arrangement the high pressure pump will be operating under substantially constant inlet pressure conditions throughout the capacity range and pump sealing may be effected with assurance.

A further feature of the present invention is that it permits the use of a single pump, or a single set of pumps, to serve the burners of more than one boiler or furnace. Thereby, only a single spare pump need be provided for the entire bank of boilers, rather than a spare pump for each boiler as required in prior art systems.

With the foregoing in mind, it is an object of the pres ent invention to provide a novel oil supply system and method of operation for wide-range return-flow mechanical fuel burner atomizers.

Another object is to provide such a system and method capable of varying the ratio of supply pressure to return pressure in accordance with variations in the oil supply pressure or rate.

A further object is to provide such a system and method with which the inlet pressure to a liquid fuel supply pump is maintained at a substantially constant value.

Still another object is to provide such a system and method with which the ratio of supply and return pressures can be varied at Will and the supply pressure and l'e'illll'n pressure controlled either manually or automatica y.

These and other objects, advantages and novel features of the invention will be apparent from the following dedescription and the accompanying drawings. In the drawings:

Fig. 1 is a schematic illustration of a Wide-range return flow mechanical fuel burner atomizer fuel system embodying the invention;

Fig. 2 is an axial sectional view through a return-flow atomizer to which the principles of the invention are applicable;

Fig. 3 is a schematic illustration of another embodiment which the invention may take in practice;

Fig. 4 is a schematic illustration of the invention system as automatically controlled in response to load demand and including continuously operable differential flow adjusting means; and

Fig. 5 is a set of curves illustrating the operation of the invention system and method.

In the drawings, and as shown more particularly in Figs. 1 and 2, the invention method and system are illustrated as applied to wide-range return-flow mechanical fuel burner atomizers generally indicated at 10. The atomizing components are arranged within a tube or distance piece 11 having its furnace or forward end carrying thereon an impeller plate 12 positioned immediately behind a fuel burner port 13 in the furnace wall 14. Tube 11 is threaded into a coupling member (not shown) Within a sleeve casing 15 supported on a mounting plate or cover 16 in the front 17 of the burner windbox.

The coupling member has fuel inlet and return passages connected, respectively to conduits or tubes 21 and 22 threaded into the atomizer head 30. Head 30 may be of the type described and claimed in the copending application of L. W. Heller, Serial No. 115,013, filed September 10, 1949, for Atomizer. Tube 21 is concentric with and of larger diameter than tube 22, so that the tubes form a central fuel outlet passage 20, defined by the tube 22, surrounded by an annular fuel inlet passage 25 between tubes 21 and 22.

The furnace end of tube 22 is threaded into a cylindrical primary nozzle or plug member 23 having a sealing contact with the furnace ends of tubes 21 and 22. Primary nozzle 23 has an annular slot 24 in its furnace face connected by a circular series of passages 26 to annular fuel inlet passage 25. The furnace face of the primary nozzle also has a smaller diameter annular slot 27, defining a central protuberance 28 and connected by a circular series of apertures 29 to the central fuel outlet or return passage 20. Protuberance 28 has a furnace face 31 which may be substantially flat or may have any other desired configuration.

The furnace face of primary nozzle 23, when atomizer 30 is assembled, contacts with the outer face of a secondary nozzle or intermediate plate 32. The latter has a central passage therethrough defined by a forwardly flaring frustoconical surface 33 connected to a rearwardly flaring frusto-conical surface 34 by a short cylindrical throat. Surface 33, with the furnace face of protuberance 28, constitute the substantially frusto-conical portion of a mixing or whirl chamber 35. The surface 34 is radially spaced from the lateral surface of protuberance 28 to form an annular passage 36 around protuberance 28 connecting whirl chamber 35 to slot 27, the relation of parts 28 and 34 being such that the walls of passage 36 diverge rearwardly. An annular slot 37 is formed in the furnace face of intermediate plate 32 in alignment with slot 24 and connected therewith by a circular series of short passages 38.

The furnace face of plate 32, beyond slot 37, contacts with the outer face of a sprayer or orifice plate, or outer tip 40, which has a portion of its periphery cut away to provide a seat for an end cap 41 which is screwed on the outer tube 21 to hold the primary nozzle, intermediate plate and sprayer plate in their desired assembled position. Sprayer plate 40 has a central cylindrical passage 42 coaxial with surface 33 to form the intermediate or main section of Whirl chamber 35. Passage 42 is connected by a frusto-conical passage 43 to a discharge orifice 44 of smaller diameter than passage 42. The outer face of sprayer plate 40 is formed with a plurality of slots 46 each tangential to the periphery of passage 42 and communicating, at their outer ends, with slot 37 of intermediate plate 32, to receive liquid fuel from slot 37 and deliver the same substantially tangentially to the central portion of the whirl chamber.

With the foregoing construction, liquid fuel, preferably oil under a substantial pressure, is delivered to inlet passage 25 from which it passes through holes 26, slot 24, holes 38 and slot 37 into tangential slots 46 in orifice plate 40. Due to the tangential arrangement of slots 46, the oil follows a spiral path in whirl chamber 35 towards discharge orifice 44. In return flow atomizer constructions, a portion of the fuel is by-passed and returned to the reservoir or the fuel pump inlet to vary the capacity of the burner. In the present atomizer head 31), such bypassed or return oil is drawn off near the outer end of Whirl chamber 35, passing through passage 36, slot 27 and holes 29 into return oil passage 20.

The flow of air through burner port 13 is controlled by air doors 47 pivotally supported between casing 15 and annular or ring member 48 mounted outwardly of the burner port. The degree of opening of doors 47 may be controlled by suitable adjusting mechanism (not shown) having operating means mounted on the outer face of plate 16.

The air controlled by doors 47 enters the furnace through a port structure 50 which may be of the type described and shown in the copending application of T. B. Stillman and J. A. Mason, Serial No. 167,992, filed June 14, 1950, now Patent No. 2,669,296, issued February 15, 1954, for Burner Throat with Air Inlet Annulus Defined by Internally Bladed Cone. As shown, the twin cone port structure 50 comprises an outer substantially frustoconical ring 51 on the periphery of port 13 and an inner frusto-conical ring 52 held in spaced relation to ring 51 by suitable means such as posts or spacers 53. Inner ring 52 axially overlaps the rim of impeller 12 and carries a series of sector-shape blades 54 on its inner surface. A second series of blades 56 are carried on the inner face of ring 51 and engage the outer surface of ring 52. Blades 54 and 56 are preferably mounted at an angle of substantially 55 to axial planes intersecting rings 51 and 52, and impart a whirling motion to the air having the same rotational direction as the oil spray or cone issuing from discharge port 44. In the present case, each set of blades 54 and 56 may comprise 16 blades circumferentially spaced 22 from each other.

Having described the construction of a typical widerange return-flow mechanical atomizer fuel burner to which the invention principles of operation are applicable, reference will now be made to the oil supply and return systems shown in Figs. 1, 3 and 4. Fig. 1 illustrates a combination of oil piping, pumps and control apparatus arranged to serve a plurality of return-flow atomizers so that burner operation may be efliciently performed through a wide range of burner capacities without carbon deposition and with a relatively low rate of return oil flow, and with a fixed axial position of the atomizer.

The oil is withdrawn from a supply or storage tank 55 by a pump 60, which delivers it under pressure to a heater 65 which is customarily used to heat the oil to the degree necessary for attainment of the desired viscosity. The oil is delivered by pump 60 at a pressure and temperature such that vapor flashing at the inlet of high pressure pump 70, or within the pump, will not occur. Pump 70 raises the pressure to an extent that it may be delivered through connecting piping 61, 62, 63 and 64, and control valve 75 to the plurality of atomizers 10 at the desired maximum inlet pressure. The return-flow passages 20 of the several individual atomizers are connected by branch lines 66 to a return-oil main 67 and this main connects through control valve 80 and pipe 58 to the oil tank 55.

The method of operation and control of the apparatus depicted by Fig. 1 will be explained with respect to atomizers such as 30, which have tangential slots and orifices selected for operation through a wide range of rating with acceptable combustion efficiency results. For these conditions, an oil pressure of a predetermined value will be required in the manifold 63 for maximum capacity operation and the two pumps 60 and 70 operating in series are selected to provide such a pressure while providing for the pressure drop through the connecting piping and control valve 75. Fig. 5 depicts the relation of desired oil pressures in supply header 63 and return header 67 in a specific installation and as measured and indicated by respective gauges 68 and 69.

For maximum or full rating operation of the atomizers, the control valve 80 on the discharge from the return header 67 is closed, while the control valve 75 is opened to affect the desired pressure in the supply header 63. Under such arrangement, the atomizer will operate as a straight mechanical atomizer without any return oil flow. Observation of the pressure gauge 69 of an operating installation of the described capacity has shown that the whirl chamber static pressure is of the order of 740 p. s. i. if the supply pressure is of the order of 1000 p. s. i., for example, and the atomizers operate with a pressure differential of 261 p. s. i. between the supply header and the whirl chamber at such supply pressure.

For effective wide range operation down to a minimum capacity, a predetermined reduction of pressure differential between the supply header and the whirl chamber is obtained, as shown by curve C of Fig. 5, through manipulation of both of the control valves 75 and 80.

In the installation from which the operating characteristics of Fig. 5 were obtained, the desired relation of supply pressure to whirl chamber pressure, as determined by the relative indications of gauges 68 and 69, is obtained in the fuel burning range from 4500 lbs. per hr. down to approximately 2500 lbs. per hr. by the throttling of valves 75 and 80. However, the latter valve is opened to such a slight degree that the amount of return oil flow is so small that it is not possible to determine its rate by the customary orifice meter and so the curve D is not extended to show return oil flow for the higher output range.

However, below a 2500 lbs. per hr. rate, and in order to avoid undue reduction in the velocity of oil introduction through the tangential slots 46 into the whirl chamber while reducing the rate of delivery to the furnace, control of the pressure differential is further effected by simultaneous manipulation of valves 75 and 80, through progressive throttling of the supply by control valve 75, while progressively manipulating valve 80 to permit a progressive increase in return oil fiow. The rate of return oil flow for the lower range of burner output, below 2500 lbs. per hr., is shown by curve D of Fig. 5. This correlated regulation of valves 75 and 80 results in a relationship as shown by curve A for supply pressure and curve B for the return or relative whirl chamber pressure. Curve 0 depicts the relative differential between these two pressures.

Thus the invention provides a method of straight mechanical atomizer operation at maximum burner output, and return flow operation from the maximum rate down to the minimum. As before stated, the rate of return oil flow at a burner rate above 2000 lbs. per hr., for example, is negligible and the rate of return oil flow at the minimum burner rate does not rise to a troublesome quantity, as will be clear from curve D. On the other hand, the reduced pressure differential, occurring through the lower rate burner output range, avoids a wide spray angle from the atomizer.

The amount of oil recirculated to tank 55 is substantially less at any atomizer delivery rate than with other prior art methods of return flow atomizer control. This is graphically demonstrated in Fig. 5, wherein the curves A' and B represent the supply pressure and return pressure, respectively, of an actual operating installation using the same atomizer controlled to maintain a substantially constant differential pressure (curve C) from 2300# of oil/burner/hour to 250# of o'il/burner/hour, the supply pressure at the top rating being 1000 p. s. i. and the return pressure 870 p. s. i. It will be noted that the recirculated or return oil rate, shown by curve D, is much greater, at all ratings, than that for the invention system, as shown by curve D.

An advantageous feature of the invention system is that it permits the use of a single pump to serve the burners of more than one boiler or furnace. In prior art returnflow fuel supply systems, an individual pump has been required for the burner arrangement of each boiler, as the differential pressure has been a function of the difference between the pump inlet and discharge pressures. Thus, the discharge of the pump is connected to the burner supply lines, and the return lines have been connected to the pump inlet. This prior art arrangement is disadvantageous in that, to provide for emergencies and pump outages for inspection and repair, a spare or stand-by pump has been required for each installation.

On the other hand, with the present system the pressure differential is controlled by selective throttling of the fuel supply and return lines, and the return flow fuel is directed to the storage tank. Consequently, only one pump, or one set of pumps depending upon the furnace rating, is required for the burners of a bank of furnaces. Thus it is feasible to provide only a single spare pump for the bank of furnaces, thus greatly reducing the installation and maintenance costs of the fuel supply system.

Fig. 3 depicts an installation in which only a single pump, or a single set of pumps if the rating is too high for a single pump, is reqired to supply fuel to a bank of furnaces each served by a plurality of fuel atomizers. In this figure, each burner 10 represents the burner arrangement for a single furnace, which usually involves a plurality of burners, such as four, for example. Likewise, each valve 75 and 80 represents the supply and return flow valves for all the burners of a single furnace, and the gauges 68, 69 indicate the fuel pressures for all the burners of each furnace. This showing has been resorted to to simplify the drawing illustration.

One or more parallel connected pumps 60 are provided to deliver fuel from tank 55 and inlet manifold 71 to outlet manifold 72. In the illustrated system, four pumps 60 are shown as commonly serving all the burners of the bank of furnaces, of which one pump 60 is a spare. The number of active pumps 60 may vary from one up, dependent upon the total rating of the bank of furnaces. From manifold 72, the fuel is delivered through a back-flow preventing check valve 79, heater 65 and main 61 to the inlet manifold of the high pressure supply pump installation.

The latter may include one or more parallel connected high pressure pumps 70, depending upon the total rating of the bank of furnaces, one pump 70 being a spare to provide for emergency or servicing outages. Pumps 70 discharge into an outlet manifold 76 connected by a main 74 to the fuel supply header 63 for the bank of furnaces.

The fuel is delivered to the bank of burners for each furnace through a conduit 64 controlled by a valve 75. Valves 75 provideindividual adjustment of the fuel supply pressure for each furnace as determined by the particular fuel requirements of each furnace. The return flow from all the burners of each furnace is effected through a conduit 66 connected to return main 67 and controlled by a return pressure control valve 80. Valves 80 provide for individual adjustment of the return pressure for each furnace, depending upon individual furnace requirements. The valves 75 and 80 may be conjointly adjusted to provide a relation of burner supply pressure to whirl chamber and return pressure, for a desired fuel delivery rate from the bank of atomizers, of each individual furnace, in accordance with a relationship shown by curves A and B of Fig. 5, the respective pressures being observed by gauges 68 and 69.

As the return-oil flow through control valves 80 will be at a nominal pressure of the order of that of the oil flowing from the outlet of heater 65, the return oil flow from the several atomizers is collected in header 67 and directed through pipes 77 and 61 to the inlet header 73 of the battery of high pressure pumps 70. As before mentioned, the quantity of return oil flow is relatively low as compared with prior art control systems. The valves 75 and 80 function to throttle the oil delivered by the pumps 70, while the pumps 60 assure a substantially constant pressure in the manifold 72, heater 65, line 61, and inlet manifold 73 of pumps 70, irrespective of variations in the atomizer delivery. The only requirement in connection with the system of Fig. 3 is that, for operation as described, the predetermined constant delivery pressure of oil from heater 65 must be selected sufficiently below the atomizer outlet pressure to insure the return oil flow through connections 66, 67, and 77.

As the pressure in manifold 73 is substantially uniform over the rating range of the atomizer, the pressure on the inlet connections, and therefore on the gland seals, of pumps 70 remains correspondingly uniform, whereby seal difiiculties, which occur with hot oil pumps delivering high pressure oil at a widely variable inlet pressure, are avoided.

In the case of an installation wherein the atomizer inlet pressure is to vary downward with load reduction from a maximum pressure of 1000 p. s. i., and the whirl chamber oil pressure is correspondingly to vary from a maximum rating value of 740 p. s. i. to a value of the order of about 20 p. s. i. at the minimum atomizer rate of approximately 450 lb. of oil/burner/hour, as shown by the curves of Fig. 5, the supply pumps 60 are selected with characteristics to give an oil delivery from the heater 65 at a substantially constant pressure of the order of or slightly below 20 p. s. i., so that the return oil flow from the atomizer will not be restricted.

In Fig. 3, the return oil is normally delivered through the relatively small diameter line 77 to the relatively large diameter line 61 connected to the outlet of heater 65. Should the return oil pressure in line 77 be substantially less than that at the outlet of heater 65, a bypass arrangement including a line 78 is provided to return the oil directly to storage tank 55. Check valve 79 is provided in header 72 just ahead of the heater 65 to prevent backward flow of oil into pumps 60. In a typical example, the pressure at the outlet of heater 65 might be of the order of 25 p. s. i. and, should the return oil pressure be less than this value, the oil is returned directly to tank 55, without adversely affecting the control of the burner output.

The invention has thus far been described as applied to manual control of the supply and return pressures. Fig. 4 illustrates how the system of Fig. 1 may be automatically controlled in response to changes in fuel demand, with the pressure differential being selectively adjustable at any time. The fuel supply piping of the system of Fig. 4 is similar to that of Fig. l. The supply pressure is controlled by a balanced pressure type valve 85, having an operating stem 86, and interposed between supply lines 61 and 62. The return pressure is controlled by a balanced valve 90, having an operating stem 91, and interposed in return line 68. For the sake of simplifying the illustration in the drawing, valve 90 has been shown as a conventional balanced valve. In actual practice, in order to provide only a very slight discharge through valve 90 when it starts to open in a reduction of burner output, the valve is so selected as to have a finely graduated flow control action at least in its initial opening range of movement.

Stems 86 and 91 are adjustably connected to opposite ends of a lever 82 pivoted, intermediate its ends, between rollers 83, 83 mounted on a block 84 longitudinally adjustable relative to lever 82 by a screw 87 having an operating handle 88. By operation of screw 87, the ratio between the two arms of lever 82 may be varied at will, so as to change the ratio between the movements of stems 86 and 91 upon movement of lever 82 about its pivot point.

Lever 82 is swung in a vertical plane, to control the positions of valves and 90, in response to variations in fuel demand. For this purpose, a control pressure is applied to a line 81, in response to fuel demand, through the medium of any well known type of boiler control system, such as the Bailey Meter Companys Boiler Master Controller, for example, the operation of which is well known to those skilled in the art. The pressure from line 81 is applied to a bellows device 92 having its movable end wall connected to the operating stem 96 of a pilot valve 95. Valve 95 controls the application of pressure to the opposite sides of a piston 97 mounted in a cylinder 98, supporting bellows 92 and having its rod 93 rigidly connected to a cross bar 94. One end of bar 94 is connected to lever 82 by a link 101, and the other end of bar 94 is connected, by a spring 102, to a bracket 103 secured to the diaphragm of device 92.

In operation, as the fuel demand increases, the action of device 92 is such as to position valve 95 to apply pressure above piston 97, moving the piston downwardly to swing lever 82 clockwise. This opens valve 85 more widely and moves valve toward its closed position, with the ratio of movement of the valves being determinable by the position of rollers 83 along lever 82. Consequently, the supply pressure and the whirl chamber or return pressure are both increased in a predetermined relation preferably such that the return pressure increases at a slower rate than does the supply pressure, to thereby produce an increasing differential pressure with increasing supply pressure. As rod 93 moves downwardly, rod 94 and spring 102 allow bracket 103 to move the stem 96 downwardly, so that application of pressure to piston 97 is interrupted when the fuel demand has been satisfied.

Upon a decrease in fuel demand, piston 97 is moved upwardly to move valve 85 toward a closing position and open valve 90 more widely, thus decreasing the supply and return pressures. The relation of such decreases is such that the supply pressure decreases faster than the return pressure, so that the pressure differential decreases as the supply pressure decreases. It will be noted that the relation of the supply pressure change to the return pressure change may be varied at any time through operation of screw 87. Cessation of movement of piston 97 occurs in the same manner as described, through movement of bracket 103, to stop movement of piston 97 when the load change is satisfied.

In the invention method, a varying ditferential between the supply and return pressures is provided, such that the ditferential increases as the supply pressure increases with increase in demand, and vice versa. Thus, excessively wide spray angles at low load, with resulting splattering and building up of carbon deposits, are avoided, and the spray angle can be selected at the optimum combustion value for each rating.

While specific embodiments of the invention have been described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

I claim:

1. In a liquid fuel circulating system including a mechanically atomizing liquid fuel burner, a fuel supply line connected to the burner, and a fuel return line leading from the burner; the combination of, pump means operative to deliver fuel under pressure to the supply line; valve means interposed in the supply line between said pump means and the burner inlet to regulate the supply pressure; valve means interposed in said return line to regulate the return pressure; and mechanism operatively interconnecting said valve means and constructed and arranged to simultaneously operate said valve means to open and close the return line valve means responsive to, but at a different rate than, closing and opening, respectively, of the supply line valve means to vary the differential between the supply pressure and the return pressure in correspondence with variations in the supply pressure.

2. In a liquid fuel circulating system including a mechanically atomizing liquid fuel burner, a fuel supply line connected to the burner, and a fuel return line leading from the burner; the combination of, pump means operative to deliver fuel under pressure to the supply line; means operative to deliver fuel at a substantially constant pressure to the inlet of said pump means; valve means interposed in the supply line between said pump means and the burner inlet to regulate the supply pressure; valve means interposed in said return line to regulate the return pressure; and mechanism operatively interconnecting said valve means and constructed and arranged to simultaneousely operate said valve means to open and close the return line valve means responsive to, but at a difierent rate than, closing and opening, respectively, of the supply line valve means to vary the difierential between the supply pressure and the return pressure in correspondence with variations in the supply pressure.

3. The method of controlling the output of a mechanically atomizing return-flow oil burner including a discharge nozzle having a Whirl chamber provided with an oil discharge orifice and forming part of an oil circulating system including oil supply means for the burner and valved oil supply and oil return lines connecting the whirl chamber to the supply and return sides of the oil supply means, with restricted area tangential inlet passages connecting the oil supply line to the whirl chamber, whereby variations in the difierential between the supply line pressure and the whirl chamber pressure will produce corresponding variations in the angular velocity of oil discharged through the discharge orifice the burner being mounted in a burner port having means for directing combustion air, at a velocity corresponding to the burner output, in embracing relation to the spray cone projected from the discharge orifice; which method comprises operating at maximum designed burner output by closing the valved oil return line while variably throttling the valved oil supply line to maintain a predetermined relation of supply and whirl chamber pressures; for a reduced output, correspondingly reducing the velocity of the combustion air, reducing the supply pressure by throttling the valved oil supply line, and concurrently reducing the whirl chamber pressure by opening the valved oil return line to establish return flow; and, with further reduction of output, further correspondingly reducing the velocity of the combustion air and concurrently reducing both the supply and whirl chamber oil pressures by, respectively, further throttling the valved oil supply line and further opening the valved oil return line in a coordinated manner, with the rate of throttling the valved oil supply line being greater than the rate of opening the valved oil return line to reduce the supply pressure at a rate greater than the reduction of whirl chamber pressure; whereby the angular velocity of the oil sprayed from the whirl chamber is correlated with the velocity of the combustion air to restrict the angle of the spray cone to a value inhibiting impingement of the oil on furnace surfaces adjacent the burner port.

4. The method of controlling the output of a mechanically atomizing return-flow oil burner including a discharge nozzle having a whirl chamber provided with an oil discharge orifice and forming part of an oil circulating system including oil supply means for the burner and valved oil supply and oil return lines connecting the whirl chamber to the supply and return sides of the oil supply means, with restricted area tangential inlet passages connecting the oil supply line to the whirl chamber, whereby variations in the difierential between the supply line pressure and the whirl chamber pressure will produce corresponding variations in the angular velocity of oil discharged through the discharge orifice, the burner being mounted in a burner port having means for directing combustion air, at a velocity corresponding to the burner output, in embracing relation to the spray cone projected from the discharge orifice; which method comprises operating over the range of maximum designed burner output by closing the valved oil return line while variably throttling the valved oil supply line to regulate only the supply pressure; for a reduced output, correspondingly reducing the velocity of the combustion air, reducing the supply pressure by throttling the valved oil supply line, and concurrently reducing the Whirl chamber pressure by opening the valved oil return line to establish return flow; and, with further reduction of output, further correspondingly reducing the velocity of the combustion air and concurrently reducing both the supply and whirl chamber oil pressures by, respectively, further throttling the valved oil supply line and further opening the valved oil return line in a coordinated manner, with the rate of throttling the valved oil supply line being greater than the rate of opening the valved oil return line to reduce the supply pressure at a rate greater than the reduction of whirl chamber pressure; whereby the angular velocity of the oil sprayed from the whirl chamber is correlated with the velocity of the combustion air to restrict the angle of the spray cone to a value inhibiting impingement of the oil on furnace surfaces adjacent the burner port.

5. The method of controlling the output of a mechanically atomizing return-flow oil burner including a discharge nozzle having a whirl chamber provided With an oil discharge orifice and forming part of an oil circulating system including oil supply means for the burner and valved oil supply and oil return lines connecting the whirl chamber to the supply and return sides of the oil supply means, with restricted area tangential inlet passages connecting the oil supply line to the whirl chamber, whereby variations in the differential between the supply line pressure and the whirl chamber pressure will produce corresponding variations in the angular velocity of oil discharged through the discharge orifice, the burner being mounted in a burner port having means for directing combustion air, at a velocity corresponding to the burner output, in embracing relation to the spray cone projected from the discharge orifice; which method comprises concurrently varying the velocity of the combustion air, and the supply pressure, the return pressure, and the diiferential between the supply and return pressures, directly with variations in output; the variation in the supply pressure, return pressure, and difierential pressure being efiected by coordinated varying of the throttling of the valved oil supply and oil return lines in opposed senses, with the rate of throttling the valved oil supply line being greater than the rate of throttling the valved oil return line to reduce the supply pressure at a rate greater than the reduction of whirl chamber pressure to vary such difierential pressure; whereby the angular velocity of the oil sprayed from the whirl chamber is correlated with the velocity of the combustion air to restrict the angle of the spray cone to a value inhibiting impingement of the oil on furnace surfaces adjacent the burner port.

References Cited in the file of this patent UNITED STATES PATENTS 

